There are a number of situations where it is necessary to provide cooling in order to achieve operational efficiency and structural integrity. One situation where cooling is required is within a turbine engine.
A gas turbine engine generally comprises, in axial flow series, an air intake, a propulsive fan an intermediate pressure compressor, a high pressure compressor, a combustor, a turbine arrangement comprising a high pressure turbine, an intermediate pressure turbine and a low pressure turbine, and an exhaust nozzle. The gas turbine engine operates in a conventional manner so that air entering the intake is accelerated by the fan which produces two air flows: a first air flow into the intermediate pressure compressor and a second air flow which provides propulsive thrust. The intermediate pressure compressor compresses the air flow directed into it before delivering that air to the high pressure compressor where further compression takes place. The compressed air exhausted from the high pressure compressor is directed into the combustor where it is mixed with fuel and the mixture combusted. The resultant hot combustion products then expand through, and thereby drive, the high, intermediate and low pressure turbines before being exhausted through the nozzle to provide additional propulsive thrust. The high, intermediate and low pressure turbines respectively drive the high and intermediate pressure compressors and the fan by suitable interconnected shafts.
In such circumstances it will be appreciated that there are high temperature gas flows which impinge upon vanes and blades within an engine. Generally, the higher an engine can operate in terms of temperature the higher that engine's efficiency. Unfortunately, there are inherent limitations upon acceptable operational temperatures of the materials from which engine components such as vanes and blades are made. In such circumstances air cooling is provided in order to ensure these components remain within acceptable operational ranges.
Generally cooling jets project a flow of air taken from the compressor towards parts which require cooling. Typically these cooling jets are circular to maximise cross-section for coolant jet impingement upon the surface to be cooled. It will be understood that generally the design or specification of coolant jets is considered in a static situation whereby the coolant jet is considered as a simple column projected beyond the coolant jet with little consideration as to leakage or deflection from impingement.
Unfortunately, within a turbine engine it will be appreciated that there is generally a significant lateral draft due to impingement wash of other jets and rotation of the relative turbine engine components. This lateral draft may be perpendicular to the projection direction of the coolant air flow from the coolant jet that is to say across it. In such circumstances, there is deflection of the collimated coolant jet and there is a significant deviation from the theoretically possible degree of cooling provided by a unit coolant air flow. Clearly, the more coolant air which impinges or strikes upon the surface to be cooled the greater the cooling efficiency. In some cases, there may be so great a deflection of the coolant air flow that there is no impingement.